The trend towards more sophisticated militarized optical systems has placed a heavy burden on the design of high resolution rugged optical adjustment mechanisms. A typical laser system with two or more optical elements must be precisely aligned for efficient operation. Alignment of these elements must be maintained over a wide range of temperature, shock and vibration disturbances.
High resolution adjustable mounts used to align optical elements, incorporate either differential screws, sliding wedges or similar mechanisms. These mechanisms must provide movement of a few millionths of an inch or a few microradians to align optical components. In a typical application where an optical system would be subjected to shock and vibration disturbances, designing a mechanism with screws or wedges that has adequate stiffness is difficult and complex. A stiff mount is required to minimize angular and linear motion of supported optics.
Load paths through either screw or wedge adjustments will not provide adequate stiffness. The result is an optical system sensitive to vibration distrubances. Another problem which plagues screw or wedge mechanisms are their ability to recover after a shock load. Again, in the microradian range, minute relative motion between screw threads or other mated surfaces will result in alignment errors. To prevent this motion adds to the cost and complexity of the mechanism.
Finding an adequate method of locking the mechanism, once alignment has been achieved, is also difficult. Locking screws, nut cleats, or other devices will result in undesirable movement which must be corrected. When preload springs are used to prevent relative movement, stiffness is compromised. A stiff, simple, high resolution adjustment mechanism is needed to eliminate many of the problems associated with complex mechanisms.
This disclosure describes the application of a simple property of most materials; that is, a change in temperature will result in a change in length. If a rod, with adequate stiffness had a controlled heater embedded in the center, the rod length could be controlled by controlling the rod temperature.